Studies designed to elucidate the mechanisms in parvovirus infection and persistence and their possible role in disease have been initiated using both in vitro and in vivo model systems. Antisera against 3 new parvovirus isolates from human cells as well as 2 laboratory variants of rat virus have been prepared and characterized for our comparative studies. The two laboratory variants have been shown to differ in their ability to produce disease and one appears to require a helper function from the other in order to replicate in cell culture. The defective variant appears to contain genetic information from minute virus of mice. Studies are now in progress to characterize the DNA and proteins of these two variants and relate them to such factors as virulence and host response. Purified clones of adeno-associated virus have been produced and characterized by comparing them to wild type as well as virus isolated from cloned carrier cells. The AAV genome in the carrier cell has been shown to be integrated into the host cell DNA. The possible role of these viruses in human disease is still being investigated. BIBLIOGRAPHIC REFERENCES: Hoggan, M.D., Sears, J.F., Thomas, G.F. and Roy, A.: Biological properties of rat virus variants. Cold Spring Harbor Symposia on Parvoviruses. In press. 1977. Roy, A., Thomas, G.F., Sears, J.F. and Hoggan, M.D.: Use of IEM to demonstrate antigenic and structural differences between infectious AAV particles banding at different densities in CsCl. Cold Spring Harbor Symposia in Parvoviruses. In press. 1977.